This invention relates to signal reproduction and, more particularly, to a novel method of and apparatus for reproducing signals which have been recorded in one portion of a rotatable record medium by using, as a demodulating signal, a reference signal that has been recorded in another portion of said medium. The present invention also relates to a method of and apparatus for recording such signals on the record medium.
Rotatable record media, such as a rotatable disc, drum, or the like, have long been used as a storage device upon which modulated signal information can be stored and subsequently reproduced. As an example, a rotatable record medium is known for the storage of video signal information, such as color television signals, audio signal information, such as stereophonic signals, quadrature audio signals, and pulse-coded information. When the signal information recorded on the record medium is recovered, it is necessary to demodulate the modulated signals with a local reference signal. As is known, this local reference signal should have the same frequency and phase as the carrier upon which the signal information has been modulated.
In typical signal reproducing apparatus, a local oscillator often is used to produce the local reference carrier. In some instances, this local oscillator is synchronized with the recorded, modulated carrier. For example, when color television signals are reproduced, the recorded composite color television signal generally includes a burst signal component, and this component is used to synchronize the local oscillator. However, if the rotation of the record medium during a signal reproducing operation is subjected to spurious fluctuations, the frequency of the reproduced signals varies in a corresponding manner and the local oscillator may not be precisely synchronized with the thus reproduced modulated signal information. Where the apparatus has been used for color television signal playback, this fluctuation results in chromatic aberration of the reproduced television picture. Where other types of signal information are recorded on the record medium, such fluctuations in the rotation thereof result in other unwanted effects.